Digital imaging is creating images by using digital technology. The image is acquired from a physical scene. After acquisition, the image may be processed, compressed, stored, printed or displayed with the help of digital technology.
A breakthrough in consumer electronics has occurred during the past two decades. Many available electronic consumer items (CDs, DVDs, HDTV, MP3s and DVRs) involve converting conventional information to digital information. The digital camera differs greatly from old-style cameras that were dependent on mechanical and chemical processes. Digital cameras can be operated without electricity, yet they contain built-in computers and have the capacity to record images electronically.
Photography began with experimentation by Henry Fox Talbot toward the end of the 1830s. In the 1950s, the art of photography was enhanced with digital techniques developed by Russell A. Kirch and colleagues at the National Bureau of Standards. The team constructed a mechanical drum capable of tracing intensity variations from photos that could be fed to a SEAC computer (Standards Electronic Automatic Computer). NASA (the National Aeronautics and Space Administration) made use of digital imaging in the 1960s and 1970s to enhance photos sent to earth from spacecrafts.
With the advent of the personal computer, and in particular, the MacIntosh, with its superior graphical interface in 1984, editing images became less expensive and easier to perform. At first, digitizing a photo meant that an image had to be scanned and input to a computer. However, digital cameras became ubiquitous beginning in the 1990s, providing a way to capture images without any need for film.
Scanners and digital cameras use a charge couple device (CCD) to convert light to an electrical impulse. Dark, light and colored areas of a photograph reflect light in varied intensities. These intensities are measured by scanners or cameras and then converted to digital information. This process is known as "filtering."
Filtering records a certain amount of information to be determined by the size of the image, the bit rate (the number of bits of information used to record each color), dots (pixels) per inch and compression. Computer screens produce colors from pixels, a fixed number of them per inch. Printing a clear image may mean using a resolution of at least 300 pixels per inch, though this number may be affected by the paper quality.
The bit rate refers to the amount of information stored per pixel. The pixels of primary colors are arranged in grids of four or five. Where only one bit of information is stored in a pixel, black or white is produced. Most monitors can display 24 bits for each primary color pixel, enabling a potential display of up to 16.7 million color shades. There are also 36- and 48-bit scanners and displays.
The color models are methods for the display and measurement of color. The eye sees color according to the wavelengths of light received. Light emanating from the full color spectrum will be perceived as white while the absence of light will be perceived as black. Perceptions of light are also affected from the viewing source: computer monitor, television screen, printed page or the surface of an object.
Images may be produced by bitmap images in which pixels are mapped to a grid. This works well for capturing photos. However, when the viewer zooms into the picture, the grid may attain an unattractive blocky appearance. Vector graphics, on the other hand, employ formulae to produce lines and color. Images produced with vectors may be scaled up or down without any loss of quality.
Images with a high bit rate will be larger files that take up vast amounts of space on a computer drive and are more difficult to transmit through the Internet. Compression is a useful tool that can be employed to limit the size of images. Two common types of image compression are GIF and JPEG.
GIFs restrict the image to 256 colors. However, GIFs have the advantage of offering animation and color transparency. The compression method used by GIF, the LZW (Lempel Ziv and Welch) means that no information is discarded in the compression process but is, instead, mapped to a color palette. That means that images retain their sharpness even after compression.
JPEGs (joint photographic experts groups) use an algorithm that results in a loss of information that gives the user a smaller image with a wider range of colors (24-bit). Other compression methods have been produced. PNG (portable network graphics), for instance, combines the better features of both GIF and JPEG.